Rubber-modified styrene resin composition

ABSTRACT

A rubber-modified flame resistant styrene resin composition, which has superior heat stability and weather resistance to prevent discoloration and deterioration due to heat or light and is processed under various molding condition, is provided. The rubber-modified flame resistant styrene resin composition includes a rubber-modified styrene resin, flame retardant comprising compounds selected from a group consisting of tetrabromobisphenol-A-bis(2,3-dibromopropylether), hexabromocyclododecane and a mixture thereof, and brominated epoxy oligomer, and calcium stearate as a lubricant.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a styrene resin composition havingsuperior heat stability and weather resistance, more particularly to arubber-modified flame resistant styrene resin composition that hassuperior heat stability and weather resistance to prevent discolorationor deterioration due to heat or light and surface appearance problemsunder various molding conditions.

(b) Description of the Related Art

Styrene resins are used for various applications due to their superiormechanical properties, electrical properties, and moldingprocessibility. However, styrene resins are combustible, and their flameresistance and weather resistance are not enough for being used forelectrical or automotive components.

Flame retardants and flame retardant synergists are used to provideflame resistance to styrene resins. Typically, a halogen flame retardantand antimony trioxide flame retardant synergist are used. However, whena halogen flame retardant is used to obtain a flame resistant resin,hydrogen halide is generated from the halogen flame retardant by heat orlight and causes formation of a carbonyl group or a conjugated doublebond, crosslinkage, and breaking of molecular bonds, which are known asthe cause of discoloration and deterioration of styrene resins.Therefore, stabilizers like a light stabilizer, a UV stabilizer, and ananti-oxidant are added to solve this problem.

Korea Patent Application No. 1998-044225 discloses use of halogencompounds other than decabromodiphenyl ether and titanium dioxide toimprove the heat stability and weather resistance of rubber-modifiedresins. However, because some flame retardants are limited in improvingheat stability and weather resistance, this method cannot be applied foroffice furnishings. Additionally, as the shape of molding productsbecomes very complex, surface appearance problems, such as gas silverand black streaks are easily generated during injection molding due todecomposition gas. Therefore, superior heat stability is required toprevent surface appearance problems under various molding conditions.

Accordingly, there is a need for a rubber-modified flame resistantstyrene resin that has superior heat stability and weather resistance toprevent discoloration or deterioration due to heat or light, and can beused for various applications.

SUMMARY OF THE INVENTION

The present invention provides a rubber-modified flame resistant styreneresin composition that has superior heat stability and weatherresistance to prevent discoloration or deterioration due to heat orlight and surface appearance problems under various molding conditionsso that it can be used for wide applications.

According to one aspect of the present invention, a rubber-modifiedflame resistant styrene resin composition comprises: a) 100 parts byweight of a rubber-modified styrene resin; b) 0.2 to 20 parts by weightof a flame retardant: and c) 0.1 to 3 parts by weight of calciumstearate as a lubricant. The flame retardant comprises i) 0.1 to 10parts by weight of compounds selected from a group consisting oftetrabromobisphenol-A-bis(2,3-dibromopropylether),hexabromocyclododecane and a mixture thereof; and ii) 0.1 to 10 parts byweight of a brominated epoxy oligomer.

According to another aspect of the present invention, a method forpreparing a frame retardant styrene resin composition, comprisescopolymerizing a rubber phase polymer and a vinyl aromatic monomer toprepare a rubber-modified styrene resin; adding a flame retardant to 100parts by weight of the rubber-modified styrene resin, the flameretardant including: 0.1 to 10 parts by weight of compound selected froma group consisting of tetrabromobisphenol-A-bis(2,3-dibromopropylether),hexabromocyclododecane and a mixture thereof; and 0.1 to 10 parts byweight of a brominated epoxy oligomer; and adding a lubricant including0.1 to 3 parts by weight of calcium stearate to 100 parts by weight ofthe rubber-modified styrene resin.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, the present invention is explained in more detail.

According to exemplary embodiments of the present invention, when ahalogen flame retardant comprising a compound selected from a groupconsisting of tetrabromobisphenol-A-bis(2,3-dibromopropylether),hexabromocyclododecane and a mixture thereof, and a brominated epoxyoligomer, and a lubricant comprising calcium stearate are added in arubber-modified styrene resin, the heat stability and weather resistanceof a rubber-modified flame resistant styrene composition are improvedsignificantly.

The rubber-modified flame resistant styrene composition of the presentinvention comprises 100 parts by weight of the rubber-modified styreneresin, 0.2 to 20 parts by weight of the flame retardant and 0.1 to 3parts by weight of calcium stearate lubricant. The 0.2 to 20 parts byweight of flame retardant comprises 0.1 to 10 parts by weight of acompound selected from a group consisting oftetrabromobisphenol-A-bis(2,3-dibromopropylether),hexabromocyclododecane and a mixture thereof, and 0.1 to 10 parts byweight of brominated epoxy oligomer.

The rubber-modified styrene resin used in the present invention has arubber phase polymer of which particles are dispersed in a matrix andvinyl aromatic monomers.

As the vinyl aromatic monomer, styrene compounds are predominantly used,and a copolymer of styrene compound and compound that can becopolymerized therewith can also be used. For the styrene compound,styrene; a nucleus-alkyl-substituted styrene such as p-methylstyrene,2,4-dimethylstyrene, or ethylstyrene; or an α-alkyl-substituted styrenesuch as α-methylstyrene or α-methyl-p-methylstyrene can be used alone orin combination. As the compound copolymerizable with the styrenecompound, a methacrylate ester such as methyl methacrylate or ethylmethacrylate, unsaturated nitrile compound such as acrylonitrile ormethacrylonitrile, or maleic anhydride, etc. can be used.

For the rubber phase polymer, a rubber phase polymer comprisingpolybutadiene, an acrylate or methacrylate, a styrene-butadiene-styrenecopolymer, a styrene-butadiene copolymer, polyisoprene, abutadiene-isoprene copolymer, or a natural rubber, etc. can be used.Particularly, polybutadiene or a styrene-butadiene copolymer ispreferable, and polybutadiene is more preferable. As the polybutadiene,a low-cis polybutadiene, a high-cis polybutadiene, or a mixture thereofcan be used.

Preferably, the rubber phase polymer is contained in an amount of 3 to30 parts by weight, more preferably 4 to 15 parts by weight, based on100 parts by weight of a rubber-modified styrene resin. If the contentof the rubber phase polymer is less than 3 parts by weight, the impactresistance becomes insufficient, and, if it is over 30 parts by weight,the heat stability may decrease, or a decrease in melt fluidity, gelformation, and discoloration may be caused. Preferably, an averageparticle diameter of the rubber phase particles is 0.5 to 6 μm, and theglass transition temperature (T_(g)) of the rubber phase polymer is −10°C. or less. If the glass transition temperature is over −10° C., theimpact resistance may decrease.

The rubber-modified styrene resin can be polymerized by bulkpolymerization, suspension polymerization, or emulsion polymerization.Particularly, bulk polymerization is the most prevalent. In bulkpolymerization, after dissolving the rubber phase polymer in the vinylaromatic monomer, polymerization is conducted by adding a polymerizationinitiator with stirring.

Tetrabromobisphenol-A-bis(2,3-dibromopropylether) andhexabromocyclododecane, flame retardants used in the present invention,are represented by the following Chemical Formula I and Chemical Formula2, respectively. They offer flame resistance to the rubber-modifiedstyrene resin.

Tetrabromobisphenol-A-bis(2,3-dibromopropylether) andhexabromocyclododecane may be used in the rubber-modified flameresistant styrene resin composition alone or in combination.

The compounds selected from a group consisting oftetrabromobisphenol-A-bis(2,3-dibromopropylether),hexabromocyclododecane and a mixture thereof are preferably contained inan amount of 0.1 to 10 parts by weight, more preferably 1 to 8 parts byweight, based on 100 parts by weight of the rubber-modified styreneresin. If the content is less than 0.1 parts by weight, flame resistancebecomes insufficient, and, if it exceeds 10 parts by weight, mechanicalstrength and heat stability may be poor.

The brominated epoxy oligomer, another flame retardant used in thepresent invention, is represented by the following Chemical Formula 3.It offers flame resistance and heat stability to the rubber-modifiedflame resistant styrene resin.

In Chemical Formula 3, n is an integer of 0 to 10.

The brominated epoxy oligomer is preferably contained in an amount of0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight,based on 100 parts by weight of the rubber-modified styrene resin. Ifthe content is less than 0.1 parts by weight, flame resistance and heatstability become poor, and, if it exceeds 10 parts by weight, mechanicalstrength may decrease.

Calcium stearate, a lubricant used in the present invention, isrepresented by the following Chemical Formula 4:

Preferably, the calcium stearate is contained in an amount of 0.1 to 3parts by weight, based on 100 parts by weight of rubber-modified styreneresin. If the content is less than 0.1 parts by weight, the heatstability may not be insignificantly improved, and, if it exceeds 3parts by weight, mechanical strength may be significantly reduced.

The rubber-modified flame resistant styrene resin composition of thepresent invention may further comprise compounds selected from a groupconsisting of antimony trioxide, antimony pentoxide and a mixturethereof as a flame retardant synergist. The flame retardant synergistcauses synergy with halogen compounds used as flame retardants tofurther improve flame resistance.

Preferably, the flame retardant synergist is contained in an amount of0.01 to 15 parts by weight, based on 100 parts by weight of therubber-modified styrene resin. If the content is less than 0.01 parts byweight, synergy with the halogen compound may be insignificant, and, ifit exceeds 15 parts by weight, mechanical strength may be significantlyreduced.

In addition, the rubber-modified flame resistant styrene resincomposition of the present invention may further comprise otheradditives such as a UV stabilizer and titanium dioxide, in order toimprove weather resistance.

For the UV stabilizer, 2-(2-hydroxy-5-methylphenyl)benzotriazole,2-(3,5-di-t-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole orbis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate, etc. can be used aloneor in combination. The UV stabilizer can be preferably used in an amountof 0.05 to 1 part by weight, based on 100 parts by weight of therubber-modified styrene resin. If its content is less than 0.05 parts byweight, improvement in weather resistance cannot be expected, and, if itexceeds 1 part by weight, the weather resistance improvement effect willnot be substantial considering the added amount.

Titanium dioxide suppresses discoloration of the resin. It can be usedin an amount of 0.1 to 6 parts by weight, based on 100 parts by weightof the rubber-modified styrene resin. If its content is less than 0.1parts by weight, the effect of suppressing discoloration of the resinmay be insignificant, and, if it exceeds 6 parts by weight, mechanicalprosperities may decrease.

The rubber-modified flame resistant styrene resin composition of thepresent invention shows no discoloration or deterioration due to heat orlight, and has superior heat stability and weather resistance. Inaddition, it can be processed under various molding conditions withoutsurface appearance problems. Particularly, it can be used for lightcolored office furnishings.

Hereinafter, the present invention is described in more detail throughExamples and Comparative Examples. However, the following Examples areonly for the understanding of the present invention, and the presentinvention is not limited by the following Examples.

EXAMPLE Example 1

(Preparation of a Rubber-Modified Styrene Resin)

A monomer solution comprising 8 parts by weight of butadiene rubber, 77parts by weight of styrene, and 15 parts by weight of ethylbenzene wasprepared. 0.02 parts by weight of 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane was added to the monomer solution asa polymerization initiator. The mixture solution was fed into acontinuous polymerization system equipped with four agitated reactorslinked in series to conduct continuous graft copolymerization.Temperature of the polymerization system was 125° C. at the inlet and140° C. at the exit. The copolymerization mixture solution wastransferred to an evaporation tank to remove unreacted monomer andsolvent under the condition of 230° C. and 20 torr. The product waspelletized to obtain a rubber-modified styrene resin (HIPS) comprising 8wt % of rubber.

(Preparation of a Rubber-Modified Flame Resistant Styrene Resin)

For 100 parts by weight of the above-prepared rubber-modified styreneresin (HIPS) comprising 8 wt % of rubber, 4 parts by weight oftetrabromobisphenol-A-bis(2,3-dibromopropylether) and 2 parts by weightof brominated epoxy oligomer as a flame retardant, 1.5 parts by weightof antimony trioxide as flame retardant synergist, 0.5 parts by weightof calcium stearate as a lubricant, 0.1 parts by weight of ananti-oxidant, 3 parts by weight of titanium dioxide, and 0.5 part byweight of a UV stabilizer were added. The mixture was uniformly mixedusing a Henschel mixer. Then, it was extruded and pelletized using atwin screw extruder, and then injection-molded into a specimen.

Examples 2 to 3 and Comparative Examples 1 to 5

The procedure of Example 1 was conducted with different compositions andcontents given in the following Table 1 to prepare rubber-modified flameresistant styrene resins of the Examples 2 to 3 and Comparative Examples1 to 5.

TABLE 1 Examples Comparative Examples Classification 1 2 3 1 2 3 4 5Rubber- 100 100 100 100 100 100 100 100 modified styrene resin (HIPS)Tetrabromo- 4 — 2 6 — 4 — 2 bisphenol-A- bis(2,3- dibromo- propylether)Hexabromo- — 4 2 — 6 — 4 2 cyclododecane Brominated 2 2 2 — — 2 2 2epoxy oligomer Antimony 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 trioxide Calcium0.5 0.5 0.5 0.5 0.5 — — — stearate Zinc stearate — — — — — 0.5 0.5 0.5Titanium 3 3 3 3 3 3 3 3 dioxide UV stabilizer 0.5 0.5 0.5 0.5 0.5 0.50.5 0.5

For the rubber-modified flame resistant styrene resins prepared inExamples 1 to 3 and Comparative Examples 1 to 5, the heat stability,weather resistance, and flame resistance were measured as follows. Theresults are shown in Table 4.

a) Heat stability—The resins prepared in Examples 1 to 3 and ComparativeExamples 1 to 5 were put in a Melt Indexer cylinder at 250° C. for 30minutes, and then these resins were put in a beaker filled withdistilled water. The whiteness of the resins was evaluated with thenaked eye according to the standard given in Table 2.

TABLE 2 ⊚ Excellent ◯ Superior Δ Moderate

b) Weather resistance—Weather resistance was measured by ASTM D4459under the condition of Table 3:

TABLE 3 Strength 0.3 W/m² Light source Xenon arc Temperature 55 ± 2° C.Relative humidity 55 ± 5% Duration 300 hours

c) Flame resistance—Flame resistance was measured by ASTM D3801according to UL-94.

TABLE 4 Examples Comparative Examples Classification 1 2 3 1 2 3 4 5Heat stability ⊚ ⊚ ⊚ Δ Δ ◯ ◯ ◯ Weather 2.2 2.4 2.4 3.2 3.3 2.8 3.0 2.9resistance (ΔE) Flame V-2 V-2 V-2 V-2 V-2 V-2 V-2 V-2 resistance

As shown in Table 4, it can be identified that the rubber-modified flameresistant styrene resins of Examples 1 to 3 (which were prepared usingtetrabromobisphenol-A-bis(2,3-dibromopropylether),hexabromocyclododecane, and a brominated epoxy oligomer as a flameretardant and using calcium stearate as a lubricant according to thepresent invention) showed superior heat stability, weather resistance,and flame resistance, compared to those of Comparative Examples 1 to 5.In addition, the resins of Comparative Examples 1 and 2, whereinbrominated epoxy oligomer flame retardant was not used, showed very poorheat stability and weather resistance, and the resins of ComparativeExamples 3 to 5 using zinc stearate as a lubricant instead of calciumstearate showed very poor weather resistance.

The rubber-modified flame resistant styrene resin composition of thepresent invention shows no discoloration or deterioration due to heat orlight, and has superior heat stability and weather resistance. Also, itcan be processed under various molding conditions without surfaceappearance problems. Therefore, it can be used for light colored officefurnishings.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

1. A rubber-modified flame resistant styrene resin compositioncomprising: a) 100 parts by weight of a rubber-modified styrene resin;b) 0.2 to 20 parts by weight of a flame retardant comprising: i) 0.1 to10 parts by weight of compound selected from a group consisting oftetrabromobisphenol-A-bis(2,3-dibromopropylether),hexabromocyclododecane and a mixture thereof; and ii) 0.1 to 10 parts byweight of a brominated epoxy oligomer; and c) 0.1 to 3 parts by weightof calcium stearate as a lubricant.
 2. The rubber-modified flameresistant styrene resin composition according to claim 1, wherein therubber-modified styrene resin of a) is prepared by copolymerization of arubber phase polymer and a vinyl aromatic monomer.
 3. Therubber-modified flame resistant styrene resin composition according toclaim 2, wherein the rubber phase polymer has an average particlediameter of 0.5 to 6 μm and a glass transition temperature (T_(g)) of−10° C. or lower.
 4. The rubber-modified flame resistant styrene resincomposition according to claim 1, wherein the brominated epoxy oligomerof b) ii) is represented by the following Chemical Formula 3:

wherein n is an integer of 0 to
 10. 5. The rubber-modified flameresistant styrene resin composition according to claim 1, furthercomprising d) 0.01 to 15 parts by weight of compound selected from agroup consisting of antimony trioxide, antimony pentoxide and a mixturethereof, as flame retardant synergist.
 6. The rubber-modified flameresistant styrene resin composition according to claim 1, furthercomprising e) 0.05 to 1 parts by weight of UV stabilizer selected from agroup consisting of 2-(2-hydroxy-5-methylphenyl)benzotriazole,2-(3,5-di-t-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole,bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate and a mixture thereof. 7.The rubber-modified flame resistant styrene resin composition accordingto claim 1, further comprising f) 0.1 to 6 parts by weight of titaniumdioxide.
 8. A method for preparing a frame retardant styrene resincomposition, comprising: copolymerizing a rubber phase polymer and avinyl aromatic monomer to prepare a rubber-modified styrene resin;adding a flame retardant to 100 parts by weight of the rubber-modifiedstyrene resin, the flame retardant including: 0.1 to 10 parts by weightof compound selected from a group consisting oftetrabromobisphenol-A-bis(2,3-dibromopropylether),hexabromocyclododecane and a mixture thereof; and 0.1 to 10 parts byweight of a brominated epoxy oligomer; and adding a lubricant including0.1 to 3 parts by weight of calcium stearate to 100 parts by weight ofthe rubber-modified styrene resin.
 9. The method according to claim 8,further comprising: adding a flame retardant synergist including 0.01 to15 parts by weight of compound selected from a group consisting ofantimony trioxide, antimony pentoxide and a mixture thereof, to 100parts by weight of the rubber-modified styrene resin.
 10. The methodaccording to claim 8, further comprising: adding 0.05 to 1 parts byweight of UV stabilizer selected from a group consisting of2-(2-hydroxy-5-methylphenyl)benzotriazole,2-(3,5-di-t-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole,bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate and a mixture thereof, to100 parts by weight of the rubber-modified styrene resin.
 11. The methodaccording to claim 8, further comprising: adding 0.1 to 6 parts byweight of titanium dioxide to 100 parts by weight of the rubber-modifiedstyrene resin.
 12. The method according to claim 8, whereincopolymerizing a rubber phase polymer and a vinyl aromatic monomer isperformed by bulk polymerization, suspension polymerization, or emulsionpolymerization.
 13. The method according to claim 8, whereincopolymerizing a rubber phase polymer and a vinyl aromatic monomerincludes adding the rubber phase polymer in an amount of 3 to 30 partsby weight, based on 100 parts by weight of the rubber-modified styreneresin.